48 Brachiopoda of the Ciiieinnati Group. 



Hemipronites planoeonvexa — (Hall, 1847). 



Shell medium size, somewhat plane on one valve and convex on the 

 other, semi-oval ; hinge line usually longer than the breadth of the 

 shell further forward ; lateral extremities deflected. 



Dorsal valve flat on the umbone, and evenly convex over the centra 

 and anterior regions ; beak not distinct from the edge of the sublinear 

 area. Interior showing bifid cardinal process directed upward and 

 outward, a little flattened on the posterior faces ; sockets deep and 

 oblique ; socket ridges oblique, prominent ; mesial ridge low, round, 

 and extending to the middle of the valve while the spaces between it 

 and the socket ridges are occupied by distinct muscular scars ; whole 

 visceral cavity irregularly, longitudinally, furrowed. 



Ventral valve nearly flat, but slightly concave in the anterio-central 

 region, and convex at the beak, which scarcely projects beyond the edge 

 of the area ; beak minutely perforated ; foramen closed by a promi- 

 nent, rounded pseudo-deltidium, that is transversely striated and 

 broadly sinuous on its inner edge, for the reception of the cardinal pro- 

 cess of the other valve ; area moderately high and tapering to the lat- 

 eral extremities, making it broadly triangular, flat, and sharply inclined 

 backward. Interior showing hinge teeth well developed, sharply tri- 

 angular and divergent, while from their inner bases obscure dental 

 ridges are projected that partly encircle the usual saucer-shaped de- 

 pression for the muscular scars ; mesial ridge dividing the muscular 

 cavity small, linear ; cardinal margin prominent and sharp within on 

 each side of the hinge teeth ; vascular markings irregular. 



Surface of both valves ornamented with moderately coarse striae, 

 that usually increase by bifurcation, sometimes by intercalation, which 

 are crossed by distinct concentric lines of growth and obscure markings. 



It is found at Cincinnati, about 380 feet above low water-mark, and 

 does not seem to have a range of ten feet in thickness ; whether or 

 not it is found higher or lower elsewhere I am not informed. It is 

 reasonably abundant where found. 



For Hemipronites, Hallie (S. A. Miller), see vol. 1, page 148, of 

 this Journal, April, 1874. 



Hemipronites sulcata — (Vernuil, 1848.) 



Shell small, more than semi-circular in outhne, moderately convex, 

 subequivalve, the dorsal valve being more convex at the middle of 



